The present invention relates to an image forming apparatus wherein a blade is used for removing residual toner adhering to an image carrier, and more particularly, to an image forming apparatus equipped with a means that applies toner on the replaced fresh blade and thereby reduces frictional resistance between the blade and an image carrier.
In an image forming apparatus such as an electrophotographic copying machine, toner images formed on the surface of a photoreceptor drum are not transferred onto a transfer sheet completely, resulting in untransferred residual toners. For the continuous copying operation, it is necessary that the residual toners are removed completely by a cleaning member for cleaning. As a cleaning member, a blade made from an elastic substance such as polyurethane is used commonly. In the case of this blade, an edge of the blade is brought into contact with a photoreceptor drum to scrape off the residual toners, in which, however, the blade is required to be replaced with a fresh one for preventing insufficient cleaning caused by abrasion of the edge of the blade.
In a conventional image forming apparatus, an operator used to set on a photoreceptor drum the cleaning unit having the replaced fresh blade on the occasion of maintenance after completion of, for example, 150,000 copies. In this case, however, when a fresh blade comes in direct contact with a cleaned photoreceptor drum, there has been a possibility that the blade is damaged by the frictional resistance which is too high. Therefore, an operator used to reduce frictional resistance between them by smearing the blade with setting powder or applying toners on the photoreceptor drum.
However, replacement of blades requiring the additional jobs mentioned above has been complicated because each of the photoreceptor drum, developing unit and cleaning unit has needed to be adjusted.
When a single blade is replaced each time it is worn away on an apparatus, the replacement cycle is too short. Therefore, it has been suggested that a plurality of blades are provided on a conventional image forming apparatus, as described, for example, in Japanese Patent Publication Open to Public Inspection Nos. 51-32335 (32335/1976),58-68776 (68776/1983) and 61-1031890 (103180/1986) (hereinafter referred to as Japanese Patent O.P.I. Publication), and Japanese Utility Model Publication Open to Public Inspection Nos. 55-12241 (12241/1980) and 60-68571 (68571/1985). In the suggestion mentioned above, a plurality of blades are supported on a blade-supporting shaft, and after a predetermined amount of operation, or after a predetermined length of time, the blade-supporting shaft is rotated so that a used blade may be replaced with a fresh one.
In the blade-replacement method mentioned above, however, there has been a possibility that a blade is damaged due to frictional resistance between a fresh blade and a photoreceptor drum as stated above, when a blade is replaced automatically.
Further, the invention relates to a cleaning device equipped with a plurality of blades.
However, when a blade-supporting shaft is rotated under the condition that a blade is in contact with a photoreceptor drum, there has been fear that the surface of the drum is damaged. Further, after cleaning, in order to prevent that the photoreceptor drum is damaged or a mark of paper dust stays on the photoreceptor drum, it has been required that the pressure force of the blade against toner and paper dust squeezed between the blade and the photoreceptor is released. Thus, an operation to move a blade away from the surface of a photoreceptor drum is needed, and when the blade-moving operation is conducted concurrently with the rotation of the blade-supporting shaft, there has been fear that blades tend to be replaced at frequency that is more than necessary.
Further, the invention relates to a cleaning device wherein a blade-supporting shaft on which a plurality of blades are affixed is rotated for blade replacement. The cleaning device mentioned above is structured so that the blade-supporting shaft that holds firmly plural blades is rotated for blade replacement each time it has operated for predetermined quantity of operation or predetermined length of time. In a cleaning device of this type, the blade-supporting shaft has been rotated either manually or through a driving means such as a rotary solenoid or a driving motor, and an angle of rotation of the blade-supporting shaft has needed to be controlled strictly because the blade has been required to be in pressure contact evenly with the photoreceptor drum at the predetermined angle and pressure.
However, it has been troublesome to rotate manually the blade-supporting shaft and to adjust an angle for the shaft each time, and it has been a disadvantage, on the other hand, that a driving motor used as a driving source makes an apparatus to be large in size and complicated.
For controlling a rotation angle strictly, there is considered an arrangement wherein locking members which engage with cutouts correspond in number to blades are provided on the blade-supporting shaft as described in Japanese Utility Model O.P.I. Publication No. 55-12241 (12241/1980). However, there has been fear that locking is impossible when a stopping position of rotating cutouts is not accurate.
In a conventional cleaning device, there has been fear that toner scatters out of a device when replacing blades because no instruction was made for the rotating direction of the blade-supporting shaft.
Further, the durability of a blade varies due to the cause such as that an amount of residual toner varies depending on conditions of usage of an electrophotographic copying machine. In the case of a type of plural blades, for example, the durability of a blade used after the use of its preceding blade is shorter than that of the preceding blade by a fall of environmental condition for usage caused by lapse of time, and durability also varies sometimes depending on each blade.
When the blade replacement time is fixed independently of usage conditions of an electrophotographic copying machine, there occur problems such as that cleaning is insufficient and that the blade is replaced even when it can further be used.
Further, the conditions of an image forming apparatus are required to be checked for replacing a blade after the blade replacement time has passed. It is necessary to pay attention so that a transfer sheet may not be soiled, an apparatus may not be affected adversely, and no downtime may be caused on operation of the apparatus, all by replacement of a blade.
In a conventional cleaning device, an edge of a blade does not come into contact evenly with the circumferential surface of a photoreceptor drum when it is mounted improperly and there has accordingly been fear of occurrence of improper cleaning, because of the blade fixed on the blade-supporting shaft. It has further been complicated to affix plural blades so that all of them may be in parallel to the circumferential surface of the photoreceptor.
The invention further relates to a cleaning device wherein a blade-supporting shaft on which a plurality of blades are affixed is rotated by elastic force of an elastic member for blade replacement.
Owing to a driving source of the elastic member by which the blade-supporting shaft is urged to rotate, it is possible to make the device small in size and simple in structure. However, when elastic energy of the elastic member is given off directly, there occurs fear that toner sticking to a blade scatters outside due to rapid rotation of the blade-supporting shaft on the occasion of blade replacement. Moreover, it is necessary to charge elastic energy after rotation power has been given off due to blade replacement, because the elastic force of the elastic member is limited.